IEEE

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IEEEsHands on Practical Electronics (HOPE)

• Lesson 5 Silicon, Breadboards

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Last Week

• Capacitors
• Q CV
• Similar to batteries
• Charge exponentially
• Charging time related to RC

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This Week

• Silicon
• Properties
• Charge Carriers
• Electrons
• Holes
• Doping
• Breadboards
• Usage

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Silicon in Everyday Use

• Silicon is used today in many different
  applications. The one you are probably most
  familiar with is your computer processor.

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Insulator vs. Conductor

• Insulators do not conduct current
• Examples plastic, wood
• Conductors conduct current
• Examples metal, ionized water.

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Semiconductors

• Is there something between an insulator and a
  conductor?
• Yes. It is called a semiconductor.
• Examples germanium, silicon, carbon (diamond
  allotrope)

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Semiconductor Silicon (Si)

• Semiconductor (from wikipedia) A material with
  an electrical conductivity that is intermediate
  between that of an insulator (no free electrons)
  and a conductor (free electrons). A semiconductor
  behaves as an insulator at very low temperatures,
  and has an appreciable electrical conductivity at
  room temperature although much lower conductivity
  than a conductor.
• Semiconductors do not follow Ohms Law.

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Industrial Use

• Silicon is the most common substance used in
  modern day fabrication.

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Silicon Wafers

• They are polished to be
  smooth on one surface
• Why only one surface?
• You only build on one side
• Wafers are about .75 mm thick
• Wafers are usually made 300mm in diameter
• For non metric system users that is about 12
  inches

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Structure of Silicon

• Pure silicon forms tetrahedral bonds in a crystal
  lattice. (Each silicon atom is connected to four
  others)

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For Simplicity

• We will represent it in two dimensions by drawing
  them at 90 degree angles.

• Remember chemistry? Silicon has all covalent
  bonds so all electrons are locked in place.
• If current is defined as moving electrons, is
  this form of silicon a conductor?

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Charge Carriers

• The negative charge carrier is called an
  electron.
• There is no charge carrier equivalent of an
  electron. The electrons antimatter counterpart
  is called a positron, which cannot co-exist with
  regular matter. We can however model the lack of
  an electron as a positive charge carrier. We
  will call this a hole.

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Doping

• By adding impurities to silicon, you can alter
  its behavior.
• Impurities are elements like boron or phosphorous
  which have 3 or 5 valence electrons. When put
  into a lattice with silicon which has 4 valence
  electrons, there is either more or less electrons
  than there should be.

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Doping

• If silicon has
• more negative charge carriers
• more electrons
• doped more heavily with elements with 5 valence
  electrons
• It is considered n-type.

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Doping

• If silicon has
• more positive charge carriers
• more holes
• doped more heavily with elements with 3 valence
  electrons
• It is considered p-type.

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Doping

• By doping silicon with elements like boron (with
  3 valence electrons) there is a lack of an
  electron in the crystal lattice. This hole can
  move too. Neighboring electrons can jump in to
  fill this space, which effectively means the hole
  moved.
• Once again, there is no positive charged particle
  moving around, but we can characterize the
  absence of an electron as a positive charge.

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Doping

• Arsenic is like phosphorous. It has 5 valence
  electrons.
• If silicon is doped with arsenic, it will have
  extra electrons which can hop from place to
  place.

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Silicon

• Why do we use silicon?
• Its cheap. Sand (SiO2) is made up of silicon.
• It is well behaved and well understood
• Do they use other materials other than silicon?
• Yes, but commercially silicon has dominated.

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Breadboards

• Used to build circuits quickly
• Can salvage parts afterwards
• Does not require soldering

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Breadboards

• DO NOT SOLDER ANYTHING ON THESE!!!
• DO NOT SOLDER ANYTHING ON THESE!!!
• DO NOT SOLDER ANYTHING ON THESE!!!

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Breadboards

• Already wired on the back.
• The long rails through the entire length of the
  breadboard are wired vertically.
• Usually used to supply a reference voltage for
  your circuit

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Breadboards

• The five pin columns are wired horizontally.
• Adjacent columns of five are NOT connected
  internally. (They are two separate groups of
  five.)
• In some cases you may wish to connect it manually.

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Lab

• In todays lab we will experiment with solar
  cells and learn to build circuits on breadboards.
• Get to it!